JPS60165343A - Heat resistant cast alloy having high creep breaking strength and carburizing resistance - Google Patents

Abstract

PURPOSE:To provide the titled heat resistant cast alloy having good weldability, obtained by specifying a composition consisting of C, Si, Mn, P, S, Cr, Ni, Co, W, Al, B, Zr, Ti and Fe. CONSTITUTION:A heat resistant cast alloy contains 0.3-0.55% C, 3.0% or less Si, 2.0% or less Mn, 0.03% or less P, 0.30% or less S, 20.0-30.0% Cr, 20.0- 40.0% Ni, 5.0-20.0% Co. 0.5-6.0% W, 0.02-0.6% Al and 0.0005-0.01% B and additionally contains 0.02-0.5% Zr or 0.02-0.5% Zr and 0.02-0.5% Ti and comprises the remainder of substantially Fe and has high creep breaking strength in a high temp. region, excellent carburizing resistance and good weldability.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-resistant cast alloy used for reaction tubes and the like in the petrochemical industry, for example, a heat-resistant cast alloy used for cracking tubes for ethylene production. The present invention relates to a heat-resistant 5㎜ alloy with excellent carburization resistance and good weldability.

Conventionally, ++IIJ heat lj steel containing Ni and Or has been used as a material for the cracking tube and the like.

For example, A8'll'M, I (K2O material (0,4O-2
5Or-2o Ni-1Fe) Yaf (P40 material (0,4G-25Cr-B5Ni-remaining Fe),
Or o4C-2sOr-a 5Ni-1,5W steel is used.

Of these, IK 40 material is generally used in a temperature range of 700 to 1 ooo'c. The reason for this is that C in the elemental E, which forms a solid solution in the austenite during casting, combines with Or when heated to a high temperature, and y! 1. When they are dispersed and precipitated as fine carbides, and heated and held for a longer period of time, carbides grow and become coarser.As a result, the creep rupture strength in this state is calculated by linearly extrapolating from the short-time side data. It is a sword that has a lower value of 10.

Also) the IP40 rate is compared to the HK40 system, , , IQ
The content of i is 15% higher, and it is excellent in terms of oxidation resistance, strength, and structural stability in the high temperature range. However, if heated and held at high temperatures for a long period of time, the creep rupture strength tends to decrease (similar to K4Q material, so
Commonly used in the temperature range of 50-1050°C.

Further, Q,4C-J50r-35Ni-1,5W steel also has creep rupture properties equivalent to the above-mentioned HP 40 material, and is commonly used in the temperature range of 950 to 1050°C. Unlike the )TP4Q material, this material contains W, so due to the solid solution strengthening effect of W, the creep rupture strength decreases by 1 (P
Although υ is smaller than 404R, its strength is not sufficient.

In addition, the heat-resistant cast steels mentioned above all have a 1050 to 11
It also has the disadvantage of poor carburization resistance in a temperature range exceeding 00°C.

Therefore, as a heat-resistant casting alloy used for reaction tubes and the like in the petrochemical industry, it is desired to develop a material that has high creep rupture strength in a high temperature range and excellent carburization resistance.

Furthermore, when continuous piping is used to assemble reaction tubes such as cracking tubes in the petrochemical industry, T, I
Since arc welding such as G welding, ΔiIG bath welding, and 1-skinned arc bath welding is used, good weldability is also required for the heat-resistant 5 alloy used in reaction tubes and the like.

The present invention is a heat-resistant casting alloy that has developed a heat-resistant fiQ alloy that satisfies these requirements. The purpose is to provide.

The carburization-resistant heat-resistant casting alloy with high creep rupture strength according to the present invention has C: O, a~055%, Si: 3°0% or less, M
n: 2.0% or less, P: 0.03% or more"r, s:
o, oa% or less, Or: 20.0~a o, o%,
N1: 20.0-40.0%, CO: 50-2oo%
, W: 0.5-60%, A(1:o, o2-06%, 1
Zr containing 0.0005 to 0.01%
:oo2~0.5% or Zr: Q, Q2~0.5
% and 0.02 to 05% of l1li2 are combined, and the remainder is substantially Fe.

C: 03 to 0.55% C combines with Nb to form eutectic carbide at grain boundaries, which increases grain boundary fracture resistance and, as a result, increases creep rupture strength. For this purpose, at least 0.3% is required to obtain high creep rupture strength, especially at temperatures above 950°C. On the other hand, if C exceeds 0.55%, there will be less chance of improving creep rupture strength, and embrittlement due to Or carbide precipitation will increase, so the upper limit is 0.05%.
It was set at 55%.

, Si: 3.9% or less Si, which is mixed in a small amount from the melted raw materials, is an effective element because it increases the fluidity of molten steel and improves castability, as well as enhances the deoxidation effect. However, if it exceeds 30%, it will have a negative effect on the creep rupture strength, so the upper limit is set to 3.0%.
%.

Mn: 2.0% or less M, n deoxidizes the molten metal, and impurity elements in the molten metal S=i
What is its effect as an element that fixes and prevents hot cracking during welding? However, even if the content exceeds 20%, the effect will be small considering the amount added, so the upper limit was set at 20%.

P: 0.08% or more If the P content exceeds 0.03%, the susceptibility to hot cracking during welding increases significantly, so the first limit was set at 0.03%.

s: o, oa% or less Like P, the content of S is 0. (If it exceeds M3%,
In order to significantly increase the susceptibility to hot cracking during welding, the upper limit was set at 0.03%.

Or: 20.0~30. ．． 0% The lower limit temperature for use is near 00°C! In order to impart oxidation resistance and high temperature strength to the material from the seat, Or should be at least 20.
It is necessary to contain 0%. Furthermore, when the content exceeds 20.0%, the oxidation resistance and high temperature strength improve as the amount increases, but when the content exceeds 30.0%, the low temperature range (900
The upper limit is 30 °C or below), and the structure becomes unstable and embrittlement due to Or carbide precipitation becomes significant.
It was set to 0%.

Ni:20. O ~ 40.0% N1 forms an austenite phase together with Cr and 'e,
In addition to being an element that stabilizes austenite, 11Ut
It is an element that improves oxidizing properties and increases high-temperature strength. 70
In order to improve the above-mentioned oxidation resistance and high-temperature strength in a temperature range of 0° C. or higher, at least 200% Ni is required. When Ni is contained at 20.0% or more, oxidation resistance and carburization resistance improve as the content increases,
Stabilizes the structure (especially the degree of carbide aggregation) in high temperature regions. However, even if the content exceeds 40.0%, there is no significant effect comparable to high-temperature strength, so the upper limit was set at 40.0%.

co: 5.0 to 200% Like -Li1i2Ni, CO is an element that stabilizes austenite AI, and is effective in improving oxidation resistance and structural stability at high temperatures. Furthermore, it has an effective effect on creep rupture strength. In order to exhibit these effects, it is necessary to contain at least 50% CO. In addition, the effect described in item 1 increases as the amount of CO increases, but in the high temperature range of about 1150°C, it is sufficient to contain as much as 20% CO, and even if more CO is added, the has no effect. Therefore, CO is 5.0-20
It was decided to contain 0%.

W: 05-60% W forms a solid solution in austenite and has a solid solution strengthening effect.

This effect is recognized from a state where W is contained in an amount of about 0.5%, and increases as the content increases. However, if its content exceeds 60%, it hardens, resulting in decreased ductility in the low temperature range and poor workability and weldability. Therefore, W is 0
It was set at 5 to 60%.

Al: o, o2 ~ 0.6% The effect of AI on improving creep rupture strength is small, and if A4 exceeds 0.6%, it has a negative effect on ductility at room temperature. 0.6% or more13
And so. On the other hand, when A4 is contained in an amount of 0.02% or more, a surface film is formed when heated to a high temperature to prevent diffusion of C in the carburizing atmosphere, thereby improving carburization resistance. Therefore, the lower limit was set at 002%.

B: 0.0005 to 0.01% B suppresses the growth of secondary carbides generated in austenite and contributes to improving creep rupture strength.

The effect is recognized from 0.0005%, but 001%
If it exceeds 0.0005, it will have a negative effect on weldability.
The allowable range for B was ~0.01%.

Next, Zr and Ti will be described. The creep rupture strength of Zr increases with the amount of Zr. On the other hand, Ill i retards the growth and coarsening of Or carbide generated in austenite by reheating and improves the creep rupture strength. When each element is contained in an amount of 0.02 to 0.5%, the effect of improving the creep rupture strength is observed. Therefore, the cast alloy according to the present invention contains Zr:o, o2~0.5% and/or T: 0.02~05%.

Hereinafter, the present invention will be specifically explained with reference to Examples.

Various cast steels having the compositions shown in Table 1 were melted using a high frequency induction melting furnace. In Table 1, Notifications 1 to A3 correspond to the materials of the present invention, which were melted as materials for various tests, and A and 4 correspond to the materials of the present invention, but materials for preparing filler wire for welding ( It was melted as A.

In Table 1, IFr, 11 and Notification 12 correspond to conventional materials, which were melted as materials for each test, and
1B corresponds to the conventional method, but was melted as a filler wire for welding.

The above cast steel was subjected to centrifugal casting to obtain an outer diameter of
Cast steel pipes with a wall thickness of 23.5 mm and a length of 520 mm were obtained, test pieces were prepared from each, and a creep rupture strength test and a carburization resistance test were conducted. The above creep rupture test was conducted for two purposes: to compare the inventive material with conventional materials, and to compare welding materials and welded joints in order to examine the weldability of the inventive material. .

Note that manual TIG welding (downward welding) was used as the final welding method to obtain the above-mentioned scrap joint. That is, A in Table 1
A predetermined beveling process (bevel angle:
20°), butted the ('d materials) together, and then using a filler wire made by cutting out and stretching the material consisting of flat 4 or 13 in Table 1, welding under the specified welding conditions (welding current:
Manual 'I'IG welding was performed at 100-V6oh, welding voltage: 14-18V, welding speed: 5, 5-8.0 m, 7 minutes) to obtain the above-mentioned welded joint.

The creep rupture test was conducted based on the provisions of JIS Z 227.2 (test temperature: 1098°C). In addition, for the carburization resistance test, a specimen (diameter 12 x length 6QMII
) in a fixed carburizing agent (Tegusa KGg'0) at a temperature of 115
After holding at 0'C for 200 hours, 0.25
Chips were collected from the pitcher and chemically analyzed, and 1.
A method was used to evaluate the carburization resistance by increasing the amount of carbon at the position of the shoe.

The test results are shown in Figure 1 (creep rupture properties of conventional material), Figure 2 (creep rupture properties of the present invention material), Figure 3 (creep rupture properties of the welded joint of the present invention), and Table 2 (creep rupture properties of the welded joint of the present invention). Fig. 1 also shows the creep rupture characteristics of the welded joint of the conventional material.

Table 2 From the test results, the long-time open side creep rupture strength of the conventional material is lower than the value linearly extrapolated from the short-time side data (see Figure 1). The long-term creep rupture strength of the invented material did not decrease as much as the conventional material (
(See Figure 2). In addition, the welded joints of conventional materials show a strength decrease of about 10% compared to the base metal (see Figure 1 ij@), but the welded joints of the present invention have the same strength as the base metal. It was found that the material of the present invention has good weldability. Furthermore, regarding carburization resistance, the carbon content of the present invention material at a position 1 mm from the surface is 55% higher than that of conventional materials.
It was found that the carburization resistance was significantly improved.

As detailed above, the n1it heat cast alloy of the present invention has higher creep rupture strength in high temperature ranges, excellent carburization resistance, and good weldability compared to conventional heat-resistant cast steels containing Ni+Or. Therefore, it is ideal as a material for cracking tubes used in the petrochemical industry, and can also be used as a material for reformer tubes, tube supports, etc. In addition, various steel-related equipment department paulownia, such as hearth rollers, radiant tubes, etc.
It is also extremely useful as a material for heat treatment trays.

[Brief explanation of the drawing]

Figure 1 is a graph showing the creep rupture characteristics of conventional H, Figure 2 is a graph showing the creep rupture characteristics of the invention material, and Figure 3 is a graph showing the creep rupture characteristics of the material of the present invention.
The figure is a graph showing the creep rupture characteristics of the welded joint of the material of the present invention in comparison with the parent phase. Stone time (Hrs) Armpit time (Hrs) Carpet time (Hrs)

Claims (1)

[Claims] (1) c: o, a ~, 0.55%, S: a, O% or less,
Mn':2. Q% or less, P: 0.08% or less, S: 0.
03% or less, Cr:2o, o ~ ao, 0%, N1:2
0.0~40.0'A, Co: 5.0~20.0%
, W: 05-60%, A#: 0.02-0.6%, 13
: Contains 0.0.005-0.01%"2,zr
:002 to 0.5% or Zr: 0.02 to 0.5% and Ti: 0.02 to 0.5%, and the remainder is substantially F.
1 carburization-resistant heat-resistant time-formed alloy with high creep rupture strength.